In the years leading up to that, Spalding and Frisén pioneered a new field of research, using the Cold War bomb pulse to answer a number of questions about human physiology, including neuron formation and lipid cycling.
The bomb pulse has been declining since the 1963 above-ground test ban treaty, creating a sort of clock they could exploit.
By determining how many radioactive carbon atoms a cell contained, Spalding and Frisén hoped they could calculate its birthdate. Spalding’s curiosity eventually leading her to a slaughterhouse on the outskirts of Stockholm.
What was once a seven-proton nitrogen became a six-proton carbon.
But unlike most carbon atoms, which have six protons six and neutrons, this radioactive carbon, known as C, scientists use a technique called mass spectrometry, which sorts atoms by weight.
Their work has been so fruitful that it could provide them with a lifetime worth of projects.
But she and her collaborators can’t waste any time.Standing outside the low, gray industrial building, she watched as horses went in one side and, about 15 minutes later, a worker appeared on the other end, holding a head, neurons and all.“It was precisely as revolting as it sounds,” she says.“In order for this to have significance, we needed to know whether this occurred in humans.” To identify dividing cells in mice and rats, Gage had been using a molecule known as bromodeoxyuridine, or Brd U.Brd U is a synthetic nucleoside that can be incorporated into newly synthesized DNA in place of the standard nucleoside thymidine, the T in ATCG.The human hippocampus, Spalding and Frisén discovered, was continually creating small numbers of neurons.